I do a lot of PDF technical document reading where I'm constantly flipping back and forth between various document sections. Although my favorite PDF viewer of choice, PDF XChange Viewer, rocks the house for annotating, searching, saving, etc., it sucks when it comes to intra-document navigation. It's got bookmarks and capabilities to run multiple instances, but I haven't liked the navigation these implement. I've also tried using multiple copies of my documents and gotten that to work the way I liked (ie. tabbed document browsing), but having multiple copies seems like a real waste to me.
Using Chrome tabs, you can easily and quickly open up multiple instances of a document by using the address bar to navigate to the local file. From there, just right-click and select duplicate. You end up creating multiple instances of PDF XChange Viewer in this case, but the navigation is SOOOO much better than clicking on the Windows taskbar.
You may have to disable the built-in PDF Viewer in Chrome to get PDF XChange Viewer working. To do this, enter "chrome://plugins" and simply disable "Chrome PDF Viewer".